As is generally known for systems and/or networks complying to the current SDH (Synchronous Digital Hierarchy) and SONET (Synchronous Optical Network) standards and, in particular, according to the International Telecommunication Union ITU standard concerning SDH and/or SONET-based signals, the multiplexing and the demultiplexing of such signals is restricted to the payload data incorporated in these SDH/SONET signals. Thus, the overhead data carrying information, in particular information concerning maintenance and multiplex protection, is always terminated by the associated section termination function implemented in the respective network elements.
As a consequence, the maintenance and protection capabilities are restricted to the respective sections where they are carried and, in particular, to the optical section, the regenerator section, and/or multiplex section, but not along the service path itself.
A functional model of a SDH/SONET multiplexer according to known standard SDH/SONET terminations is shown, for example, in the appended FIG. 10. As can be seen therefrom, for each standard port 1 to “n”, the optical, regenerator and multiplex section layers of the SDH/SONET signals are always terminated by the associated standard optical section OS, regenerator section RS, and multiplex section MS termination functions, respectively. The connectivity based on the connection functions for STSNC (S3/S4) and the transparent transport of data is therefore limited to the VC/STS (Virtual Container/Synchronous Transport Signal) payload embedded within the server signals or carriers, in particular, within optical carriers.
A disadvantage of this architecture is that SDH/SONET systems are not able to transport the SDH/SONET signals as a service and, in particular, as an end-to-end service. As is known, end-to-end services over SDH/SONET networks are always restricted to the associated payload.
Moreover, with regard to a usual application according to the known state of the art, FIG. 11 depicts a common carrier application based on known SDH/SONET and all-optical transmission solutions. According to the depicted exemplary application, a metropolitan network operator has two metropolitan SDH/SONET networks NCA connected via a second operator's core network NCC, which consists of SDH/SONET network elements 10 and optical cross connect and/or DWDM (dense wavelength division multiplex) equipment 20. The metropolitan networks NCA merely consist of SDH/SONET network elements 10, in particular, SONET/SDH cross connect and/or add/drop multiplexer network elements.
As the signals in the carrier network NCC have to cross standard SDH/SONET equipment 10 at least at the handoff points 202 between the respective networks, only SDH/SONET payload connectivity between the two metropolitan networks NCA is possible. As a consequence, the two networks NCA are islands in terms of network management and line protection schemes. Moreover, since the metropolitan network NCA operator only uses SDH/SONET network elements 10, the service which he can offer between the respective service interfaces 201 is also restricted to SDH/SONET payload only, regardless if the service has to cross the carrier network NCC or not.
Thus, the need of also transporting the SDH/SONET signal itself as a service is foreseen and already strongly requested from several network operators. One approach to support this could be the introduction of a separate optical layer. However, there would be disadvantages associated with the introduction of completely new families of products.
Moreover, even if the carriers carrier network NCC is changed into an all-optical network, as depicted in FIG. 12, i.e., merely having optical cross connect and/or DWDM equipment 20 which is capable of transporting SDH/SONET signals including the SDH/SONET overhead data, the two metropolitan networks NCA are still not able to offer SDH/SONET signals as an end-to-end service between the service interfaces 201 due to the use of standard SDH/SONET cross connect and/or add/drop multiplex equipment 10. However, the operator of the metropolitan networks NCA gain the ability to connect the two network islands NCA in terms of network management and line protection schemes, when the carrier network NCC is introducing such an all-optical network according to FIG. 12, and is not gaining anymore from the SDH/SONET-based network NCC, as depicted in FIG. 11.
Furthermore, in addition to these above mentioned problems, a further very important issue with traditional SDH/SONET systems exists on transoceanic transmission. As is generally known, transoceanic transmission systems need standard SDH/SONET framed signals as input, which are wrapped into a proprietary frame including very strong forward error correction (FEC) schemes that enable them to transmit over very long distances without the need of signal regeneration. However, because bandwidth per lambda (wavelength) also determines the cost of transoceanic transmission, transoceanic systems are driven to 10 Gigabit transmission per lambda. On the other hand, there is a strong market need to support 2.5 Gigabit, transparent SDH/SONET services across the ocean.
One known way to support transparent 2.5 Gigabit services is to employ proprietary multiplexing of 4 times 2.5 Gigabit SDH/SONET signals and to then wrap this 10 Gigabit signal along with additionally added FEC for transport as a signal via a lambda (wavelength). Since the 10 Gigabit output signal is incompatible with a 10 Gigabit SDH/SONET signal, there is no way to transport this signal over transoceanic systems.